Namely, the behaviour of the Magic Wand tool is different from what I expect. It always selects all pixels of the same colour in a layer even if the area is not contiguous. This happens regardless of parameter values: tolerance, anti-alias, and contiguous. The effect is like that of some kind of a "select by colour" tool.

Just to make sure:

- I am on the correct layer

- I am using the correct tool (Magic Wand, not Quick Selection Tool)

- I have tried exiting CS5 and starting it again

- I have tried resetting the Magic Wand Tool

- I am trying to make a new selection (not adding to it, subtracting from it or intersecting with it)

The conclusions from my little research are that this bug (?) goes as far as CS3. Back then there was a trick to change the Sample Size of the Eyedropper tool, which had been reported to work. Apparently it does not work in CS5 anymore.

Back then there was a trick to change the Sample Size of the Eyedropper tool, which had been reported to work. Apparently it does not work in CS5 anymore.

Assuming you're talking about the Magic Wand Tool selecting colors based on a sample of more than one pixel, the same thing still applies in Photoshop CS5: The sample size you choose, for example with the Eyedropper Tool, still affects the Magic Wand's sampling to determine what pixel(s) to select. That's not a bug, it's a feature.

Yes. I have tried with Contiguous checkbox both checked and unchecked. The problem is now solved as, suprisingly, "Sample All Layers" turned out to be the cause. It had to be checked in my case for the Magic Wand to work correctly.